FIG. 11 is a sectional view of a conventional capacitor, and FIG. 12 is a sectional view illustrating a structure of pressure regulating valve 23 provided in the capacitor. This capacitor includes capacitor element 20 provided with hollow 20A. Capacitor element 20 includes a pair of positive and negative electrodes, in each of which polarizable electrode layers are formed on an aluminum foil current collector, and a separator is interposed therebetween (not illustrated). The positive and negative electrodes are wound in such a manner that they are displaced from each other in the opposite direction (in the vertical direction in FIG. 11). From both ends (upper and lower ends in FIG. 11) of capacitor element 20, positive and negative electrodes are electrically led out, respectively.
Cylindrical case 21 with a bottom made of a metal, such as aluminum, houses capacitor element 20 together with electrolyte (not illustrated). Negative terminal 21A for external connection is provided integrally on the outer bottom face of case 21. Protrusion 21B is provided integrally on the inner bottom face of case 21 so that protrusion 21B is fitted into hollow 20k After protrusion 21B is fitted into hollow 20A, an end face of the negative electrode side in capacitor element 20 that is inserted into case 21 is mechanically and electrically bonded to the inner bottom face of case 21, typically by laser welding.
Positive terminal 22A for external connection is integrally provided on the outer face of aluminum sealing plate 22. Protrusion 22B is fitted into hollow 20A. Hole 22C is provided so as to allow for pouring of the electrolyte. Pressure regulating valve 23 is provided so as to close hole 22C. An end face of the positive electrode side in capacitor element 20, is mechanically and electrically bonded to the inner face of sealing plate 22, typically by laser welding. Furthermore, case 21 is sealed by bending a rim of sealing plate 22 such that the rim wraps around the opening of case 21 (curling process).
As shown in FIG. 12, pressure regulating valve 23 includes gas permeable member 24, blocking body 25, and cap 26. Gas permeable member 24 and blocking body 25 are disposed over hole 22C. Metal cap 26 is fixed so as to cover gas permeable member 24 and blocking body 25, and presses blocking body 25 in a direction that blocking body 25 always blocks hole 26k Cap 26 is provided with hole 26A that leads to outside. Annular convex part 22D is provided on sealing plate 22 around hole 22C. Cap 26 is fixed by deforming convex part 22D, typically by caulking and pressing it against cap 26.
Pressure regulating valve 23 releases gas generated inside the capacitor to the outside when the internal pressure of the capacitor reaches a predetermined pressure or above. Thus, the pressure inside the capacitor is prevented from increasing. Furthermore, after operation, pressure regulating valve 23 returns to the state before operation so as to maintain the air-tightness inside the capacitor. In other words, pressure regulating valve 23 is a self-returning type valve. Therefore, even if the internal pressure is increased due to the generation of gas inside the capacitor, the appearance of the capacitor is not affected, and the characteristic thereof can be maintained.
Furthermore, pressure regulating valve 23 includes gas permeable member 24. Gas permeable member 24 is formed of a material capable of preventing permeation of the electrolyte but allowing a gas generated inside the capacitor to permeate to the outside. By bringing gas permeable member 24 into close contact with sealing plate 22 around hole 22C, it is possible to prevent the function of pressure regulating valve 23 from being impaired due to contact of the electrolyte with blocking body 25. Furthermore, it is possible to prevent the electrolyte from leaking outside of the capacitor via pressure regulating valve 23. Such a capacitor is disclosed in, for example, Japanese Patent Unexamined Publication No. 2004-134632.
As described above, in a conventional capacitor, pressure regulating valve 23 is disposed on hole 22C provided to allow for pouring of the electrolyte. This prevents leakage of the electrolyte. However, pressure regulating valve 23 is provided by directly assembling each member over hole 22C after the capacitor is fabricated and the electrolyte is poured through hole 22C. Therefore, variations in the assembly accuracy of pressure regulating valve 23 lead to variations in the operation of pressure regulating valve 23. In particular, since an amount of compression of blocking body 25 directly affects an operating pressure of pressure regulating valve 23, variations in the operating pressure of pressure regulating valve 23 easily occur. In addition, the operation of pressure regulating valve 23 cannot be checked independently.
With respect to those for use in vehicles, more reliable capacitors are demanded due to the severe environment when used in vehicles. In particular, capacitors including a pressure regulating valve that demonstrates a high operating performance at high temperatures have been demanded.